Wireless Communication System, Transmitting Device And Receiving Device

ABSTRACT

A wireless communication system has a transmitting device and a receiving device that perform communication by using a multi-carrier signal, wherein the receiving device includes a quality generating unit generating each piece of receiving quality information on each pilot channel for transmitting each pilot signal, a determining unit determining the number of pilot channels needed in the multi-carrier signal based on the receiving quality information, and a notifying unit transmitting a signal requesting the determined number of pilot channels to the transmitting device, and the transmitting device includes an allocation unit determining allocations of pilot signals in the direction of the time axis and in the direction of the frequency axis, corresponding to a requested number of pilot channels, and a transmitting unit transmitting the multi-carrier signal having the determined pilot signal allocations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/838,956, filed Jul. 19, 2010, now U.S. Pat. No. ______, which is acontinuation of U.S. application Ser. No. 11/709,237, filed Feb. 22,2007, now U.S. Pat. No. 7,764,643.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, atransmitting device and a receiving device that perform channelestimation by use of pilot signals etc in a multi-carrier transmissionmethod.

2. Description of the Related Art

An OFDM (Orthogonal Frequency Division Multiplexing) method is adoptedas a transmission method in a variety of communication systems andactualizes high-speed data communications at high frequency availabilityefficiency. The OFDM method is defined as a method of segmentingtransmission data into plurality of data, mapping the segmentedtransmission data onto a plurality of orthogonal carrier waves(subcarriers), and transmitting the data in parallel along a frequencyaxis.

An examination of a radio frame format employed in such a type ofwireless communications is now under consideration in the 3GPP (3rdGeneration Partnership Project) etc, and FIG. 12 shows an example ofthis radio frame format. In the radio frame format illustrated in FIG.12, each frame is provided at a TTI (Transmission Time Interval)interval, wherein OFDM symbols are allocated in a frequency (an axis ofordinate)-to-time (an axis of abscissa) array within each frame.Further, each frame is generated by a plurality of subcarriers, and eachsubcarrier consists of 7 symbols along the time axis. Allocated to eachsubcarrier are a common pilot channel (Common Pilot Channel), adedicated pilot channel (Dedicated Pilot Channel) and other channels(Other Channels which will hereinafter be referred to as data channels),respectively. A pilot symbol common to all users is allocated to thecommon pilot channel, a dedicated pilot symbol assigned corresponding toeach of predetermined users is allocated to the dedicated pilot channel,and data symbols are allocated to the data channels.

In a receiving device utilizing this type of frame format, influence byfading is compensated by a propagation characteristic value (a channelestimation value) etc estimated by use of this pilot symbol. In thiscase, the fading influence is different for every symbol, and hence thereceiving device is required to interpolate the channel estimation valueon the frequency axis and on a time axis on the occasion of demodulatingeach symbol. For instance, the example in FIG. 12 illustrates that thechannel estimation value existing in each symbol position is linearlyinterpolated by use of a pilot symbol CP-1 and a pilot symbol DP-1, andsymbols 1-A and 1-B are demodulated based on the thus-obtained channelestimation value.

It should be noted that the following documents disclose theconventional arts related to the invention of the present application.The conventional art documents are “Japanese Patent ApplicationLaid-Open Publication No. 2003-032146” and “Technical SpecificationGroup Radio Access Network, “Physical Layer Aspects for Evolved UTRA(Release 7)”, 3rd Generation Partnership Project, 3GPP TR 25.814 V1.0.1,November 2005, p. 22-24.”

It is known that in the radio frame format described above, the numberof the pilot symbols and positions of the pilot symbols to be allocatedlargely contribute to communication performance such a received errorrate. For example, it follows that a transmission rate decreases thoughchannel estimation accuracy is improved in the case of increasing thenumber of the pilot symbols, and the received error rate is deterioratedwhile the channel estimation accuracy is lowered in the case ofdecreasing the number of the pilot symbols. Further, the fadinginfluence depends on a propagation environment etc, and hence, even whenusing the radio frame having the same pilot symbol allocation, thechannel estimation accuracy based on this pilot symbol allocationchanges corresponding to the propagation environment etc.

SUMMARY OF THE INVENTION

It is an object of the present invention, which was devised in view ofthe problems described above, to provide a wireless communicationsystem, a transmitting device and a receiving device that attain anexcellent error rate characteristic without depending on the propagationenvironment.

The present invention adopts the following configurations in order tosolve the problems. Namely, the present invention relates to a receivingdevice receiving a multi-carrier signal in which plural pilot signalstransmitted from a transmitting device are allocated in a direction of atime axis and in a direction of a frequency axis, the receiving devicecomprising a quality generating unit generating each piece of receivingquality information on each pilot channel for transmitting each pilotsignal, a determining unit determining the number of pilot channelsneeded in the multi-carrier signal transmitted from the transmittingdevice based on the generated receiving quality information, and anotifying unit transmitting a signal requesting the determined number ofpilot channels to the transmitting device.

In the present invention, the receiving quality information giving apropagation (channel) environment acting on each pilot channel isgenerated. This receiving quality information is exemplified such as anSINR (Signal to Interference and Noise Ratio) and a bit error rate(BER). In the present invention, the necessary number of pilot channelsin the signals transmitted from the transmitting device is determinedbased on each piece of generated receiving quality information, and thetransmitting device is notified of this determined number of pilotchannels. Herein, “the number of pilot channels to be determined” doesnot specify only the number in an absolute meaning, and any one of anincrease and a decrease in the number of pilot channels may also bedetermined.

With this contrivance, the transmitting device notified of the requestednumber of pilot channels is capable of generating the radio frame havingthe pilot configuration that meets the request. Therefore, according tothe present invention, the propagation environment can be promptlyreflected in the configuration of the pilot channels, so that it ispossible to prevent a decrease in the transmission rate due to thefutile allocation of the pilot channels while scheming to improve thecommunication performance such as the receiving error rate.

Further, in the present invention, the determining unit may determinethe necessary number of pilot channels in the direction of the frequencyaxis based on the receiving quality information on the neighboring pilotchannels in the direction of the frequency axis, and/or may determinethe necessary number of pilot channels in the direction of the time axisbased on the receiving quality information on the neighboring pilotchannels in the direction of the time axis. Information to be referredto when determining the necessary number of pilot channels may involveusing differences in the receiving quality information between theneighboring pilot channels or an average value of these differences.

Hence, according to the present invention, it is feasible to take theproper pilot channel configuration in which the propagation environmentis concretely reflected.

Still further, in the present invention, the determining unit maydetermine to increase and decrease the necessary number of pilotchannels in the direction of the frequency axis by comparing a valueobtained from the receiving quality information on the neighboring pilotchannels in the direction of the frequency axis with a predeterminedthreshold value, and/or may determine to increase and decrease thenecessary number of pilot channels in the direction of the time axis bycomparing a value obtained from the receiving quality information on theneighboring pilot channels in the direction of the time axis with apredetermined threshold value. The value compared with the predeterminedthreshold value may involve using the differences in the receivingquality information between the neighboring pilot channels or theaverage value of these differences.

Yet further, in the present invention, the determining unit maydetermine a request for an all-pilot frame by comparing a value obtainedfrom the receiving quality information on the neighboring pilot channelsin the direction of the frequency axis with a predetermined upper limitthreshold value, and/or may determine the request for the all-pilotframe by comparing a value obtained from the receiving qualityinformation on the neighboring pilot channels in the direction of thetime axis with a predetermined upper limit threshold value, and thenotifying unit may notify the transmitting device of a signal requestingthe all-pilot frame. Moreover, the value compared with the predeterminedupper limit threshold value may involve using the differences in thereceiving quality information between the neighboring pilot channels orthe average value of these differences.

In the present invention, the receiving quality information (thedifferences in each piece of the receiving quality information or theaverage value of these differences) on the neighboring pilot channels inthe direction of the frequency axis and/or in the direction of the timeaxis is compared with the predetermined upper limit threshold value,thereby determining whether the all-pilot frame is requested or not. Theall-pilot frame represents such a frame that only the pilot channels areallocated within the radio frame. With this scheme, in the case ofreceiving the signal containing this all-pilot frame, it follows thatthe receiving quality information is generated with respect to all thepilot channels, and the process of determining the number of pilotchannels as described above is executed based on all pieces of generatedreceiving quality information.

Therefore, according to the present invention, even in a case wherethere increases the difference in the receiving quality informationbetween the pilot channels, i.e., even in a case where fading exertslarge influence, the control can be conducted so as to immediately havethe proper pilot channel allocation. Hence, the control is carried outso as to take the proper pilot channel allocating configurationcorresponding to a now-and-then propagation environment, whereby thedevice can be made less likely to be affected by the fading that dependson the propagation environment etc.

Moreover, the present invention also relates to a transmitting devicereceiving a signal containing a requested number of pilot channels,which is transmitted from the notifying unit of the receiving device.The transmitting device according to the present invention may comprisean allocation unit determining allocations of pilot signals in adirection of a time axis and in a direction of a frequency axis,corresponding to a requested number of pilot channels of which areceiving device notifies, and a transmitting unit transmitting amulti-carrier signal having the determined pilot signal allocations.

With this contrivance, the transmitting device generates the radio framein which to reflect the requested number of pilot channels of which thereceiving device notifies.

Hence, according to the present invention, the propagation environmentcan be promptly reflected in the pilot channel configuration, therebymaking it possible to prevent a decrease in transmission rate due to thefutile allocation of the pilot channels while scheming to improve thecommunication performance such as the receiving error rate.

Further, in the transmitting device according to the present invention,the transmitting unit, when the receiving device notifies thetransmitting unit of a request for an all-pilot frame, may transmit themulti-carrier signal having the all-pilot frame.

With this contrivance, the receiving device becomes capable ofimmediately grasping the necessary number of pilot channels or the pilotchannel allocation based on the propagation environment.

It should be noted that the present invention also relates to a wirelesscommunication system comprising the receiving device and thetransmitting device described above. Moreover, the present invention mayalso be a program that actualizes any of functions related to thereceiving device and to the transmitting device, and may further be areadable-by-computer storage medium stored with such a program.

According to the present invention, it is possible to actualize thewireless communication system, the transmitting device and the receivingdevice that attain the excellent error rate characteristic withoutdepending on the propagation environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a functional configuration of a receivingdevice in the present embodiment;

FIG. 2 is a diagram showing an example of radio frame in the presentembodiment;

FIG. 3 is a diagram showing an example of a pilot channel allocationafter a process in Pattern 1;

FIG. 4 is a diagram showing an example of the pilot channel allocationafter a process in Pattern 2;

FIG. 5 is a diagram showing an example of the pilot channel allocationafter the process in Pattern 1 and the process in Pattern 2;

FIG. 6 is a diagram showing an increasing and/or decreasing sequence ofthe pilot channels in a direction of a time axis;

FIG. 7 is a diagram showing an all-pilot frame;

FIG. 8 is a table showing an example of notification of the pilotchannel allocation information;

FIG. 9 is a diagram showing a functional configuration of a transmittingdevice in the present embodiment;

FIG. 10 is a flowchart showing an operational example of determining thepilot channel allocation in the receiving device;

FIG. 11 is a flowchart showing an operational example of determining thepilot channel allocation in the receiving device; and

FIG. 12 is a diagram showing a format of a conventional radio frame.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A wireless communication device in an embodiment of the presentinvention will hereinafter be described with reference to the drawings.The wireless communication device in the present embodiment encompasses,e.g., a mobile terminal and a base station device (an access point) thatperform wireless communications with each other. It is to be noted thatthe following discussion shall deal with the wireless communicationdevice in the present embodiment in the way of its being categorizedinto a receiving device and a transmitting device for explanatoryconvenience's sake. The present invention is not, however, limited tothis configuration and may be applied to a communication deviceincluding both of a receiving function and a transmitting function thatwill hereinafter be explained. Throughout the discussion, aconfiguration in the following embodiment is an exemplification, and thepresent invention is not limited to the configuration in the embodiment.

[Receiving Device]

The receiving device in the embodiment of the present invention will beexplained with reference to FIG. 1. FIG. 1 is a diagram showing afunctional configuration of the receiving device in the presentembodiment.

The receiving device in the present embodiment includes a receivingantenna 100, a receiving unit 101, a serial/parallel (which willhereinafter be abbreviated to S/P) converting unit 101, a discreteFourier transform (which will hereinafter be abbreviated to DFT) unit102, a parallel/serial (which will hereinafter be abbreviated to P/S)converting unit 103, a demodulation unit 104, a channel estimation unit105, a decoding unit 106, a receiving quality information generatingunit 110 (corresponding to a quality generating unit and a determiningunit according to the present invention), a frame requesting unit 111(corresponding to the determining unit according to the presentinvention), a transmitting unit 112 (corresponding to a notifying unitaccording to the present invention), a transmitting antenna 120, etc.

The wireless communication device in the present embodiment performs thecommunications by use of a radio frame shown in FIG. 2. FIG. 2 is adiagram illustrating an example of the radio frame in the presentembodiment. In the radio frame shown in FIG. 2, one frame is formed atTTI. The frame is constructed of a plurality of subcarriers, whereineach subcarrier further consists of seven symbols arranged along a timeaxis. In the frame, common pilot channels (P1, P2, P3, etc) areallocated on a one-by-one basis to every two subcarriers at this ratioin a direction of a frequency axis with respect to the head symbols inthe direction of the time axis. In the frame, pieces of user data etcare allocated to channels (data channels) other than the pilot channels.It should be noted that the present invention does not limit asubcarrier frequency interval at which the common pilot channels arearranged.

A radio frequency signal received by the receiving antenna 100 istransmitted to the receiving unit 101. The receiving unit 101 convertsthe received radio frequency signal into a baseband signal and furtherconverts the thus-converted baseband signal into a digital signal. TheS/P converting unit 101, upon receiving the converted digital signal,converts this digital signal into a plurality of parallel signals.

The DFT unit 102 executes a DFT process about the inputted parallelsignals, and outputs a plurality of signals corresponding to therespective subcarrier components. These outputted parallel signals aretransmitted respectively to the P/S converting unit 103 and to thechannel estimation unit 105. The P/S converting unit 103 rearranges thereceived parallel signals into serial signals and thus transmits theserial signals to the demodulation unit 104.

The channel estimation unit 105 compares a pilot signal in the signalstransferred from the DFT unit 102 with a known pilot signal, therebyobtaining a channel estimation value with respect to a link to thepresent receiving device from the transmitting device. The channelestimation unit 105 detects an allocation of the pilot signal in thesignals transferred from the DFT unit 102 on the basis of pilot signalallocation information given from the frame requesting unit 111. Thispilot signal allocation information will be described later on. Thepresent invention does not limit this channel estimation method, and thechannel estimation value may also be obtained by, e.g., an operationbased on a least-squares method. The thus-obtained channel estimationvalue is defined as a propagation characteristic value related to thepilot channel to which the pilot signal is allocated. Such being thecase, the channel estimation unit 105 acquires the channel estimationvalue with respect to the data channels, to which the pilot signals arenot allocated, by a method such as linear interpolation in the directionof the frequency axis and in the direction of the time axis. Thethus-acquired channel estimation value about each symbol of eachsubcarrier is sent to the demodulation unit 104. Further, the channelestimation value obtained from the pilot signal is sent to the receivingquality information generating unit 110.

The demodulation unit 104 performs synchronous detection anddemodulation on the inputted serial signal by using the channelestimation value transferred from the channel estimation unit 105. Thethus-demodulated signals are transferred to the decoding unit 106. Thedecoding unit 106 decodes the signals from the demodulation unit 104 bya predetermined coding rate and a predetermined decoding method. Thedecoded data are outputted as receiving data to other function units.

The receiving quality information generating unit 110 generatesinformation representing a receiving quality. This informationrepresenting the receiving quality is, for example, an SINR (Signal toInterference and Noise Ratio) obtained based on the channel estimationvalue received from the channel estimation unit 105. In this case, thereceiving quality information generating unit 110 obtains the'SINR fromdesired power (S) of each pilot symbol and from interference noise power(I). The desired power of each symbol is acquired by, e.g., squaring anabsolute value of the channel estimation value, while the interferencenoise power is acquired by, e.g., taking a correlation between thereceived signal and the pilot signal.

The receiving quality information generating unit 110 may obtain a biterror rate (BER) by way of another example. In this case, the receivingquality information generating unit 110 receives cyclic redundancy check(which will hereinafter be abbreviated to CRC) bits in the data decodedby the decoding unit 106 and checks the CRC bits, thereby obtaining thebit error rate (BER) in predetermined intervals. The “predeterminedintervals” connote an interval between the two neighboring pilotchannels in the direction of the time axis and an interval between thetwo neighboring pilot channels in the direction of the frequency axis.An example shown in FIG. 2 is that the bit error rate between a symbol1-A and a symbol 1-F in the direction of the time axis and the bit errorrate of a symbol 1-G in the direction of the frequency axis, areobtained. The thus-obtained receiving quality information is transferredto the frame requesting unit 111.

The frame requesting unit 111 determines, based on the receiving qualityinformation about the pilot channels, an allocation of the pilot signalswith respect to the radio frame used for the transmission between thetransmitting device serving as a transmission partner device and thepresent receiving device. The frame requesting unit 111 determines theallocation of the pilot signals on the basis of three patterns that willbe given as below.

(Pattern 1) The number of the pilot channels in the direction of thefrequency axis is changed.

(Pattern 2) The number of the pilot channels in the direction of thetime axis is changed.

(Pattern 3) An all-pilot frame (a training period) is requested.

The frame requesting unit 111, to begin with, determines the allocationof the pilot signals on the basis of the Pattern 1. In a case where theradio frame illustrated in FIG. 2 is received, the frame requesting unit111 receives, from the receiving quality information generating unit110, each piece of receiving quality information on each of the pilotchannels with respect to the frame at TTI(n). The frame requesting unit111 obtains each difference in the receiving quality information betweenthe neighboring pilot channels in the direction of the frequency axis.The example in FIG. 2 is such that only the common pilot channels existin this frame, and hence the receiving quality information is targetedat the respective pilot channels existing in head symbols of the frame.To be specific, the differences in the receiving quality informationbetween the respective pilot channels in the direction of the frequencyaxis are acquired such as obtaining the difference between the receivingquality information of the pilot channel P1 and the receiving qualityinformation of the pilot channel P2 and further obtaining the differencebetween the receiving quality information of the pilot channel P2 andthe receiving quality information of the pilot channel P3. In the caseof increasing the number of the pilot channels in the direction of thetime axis according to the Pattern 2 that will be explained as below,the pilot channels allocated to the increased symbols are also set asthe targets.

The frame requesting unit 111, when obtaining the differences in thereceiving quality information between the respective pilot channels,further acquires an average value of these differences in the receivingquality information therebetween, and compares this average value withan upper limit threshold value retained beforehand. For instance, if thebit error rate is used as the receiving quality information, a value inthe vicinity of 0.1 may be set as the upper limit threshold value(corresponding to a predetermined threshold value according to thepresent invention). The frame requesting unit 111, if the average valueexceeds the upper limit threshold value, determines to increase thepilot channels in the direction of the frequency axis. As a result ofthe determination thus made, the radio frame to be transmitted from thetransmitting device becomes as illustrated in FIG. 3. FIG. 3 is adiagram showing an example of the pilot channel allocation to be changedas the result of the determination of the frame requesting unit 111. Theexample in FIG. 3 shows an addition of the pilot channels (P1-10, P2-10,P3-10, P4-10, P5-10) in the direction of the frequency axis with respectto head symbols of the radio frame.

Thus, the pilot channel allocation to be changed as the result of thedetermination of the frame requesting unit 111 is handled based on apredetermined unit in the radio frame. For instance, in the example ofthe radio frame shown in FIG. 2, a range containing one common pilotchannel (a range extending from the subcarrier containing P-1 to thesubcarrier containing P-2) is dealt with as one unit in each frame. Withthis contrivance, the radio frame is changed so as to have theallocation of the same pilot channel on the basis of each unit withinevery frame.

The frame requesting unit 111 retains, in addition to the upper limitthreshold value described above, a lower limit threshold value(corresponding to a predetermined threshold value according to thepresent invention). The frame requesting unit 111, when judging that theaverage value of the differences in the receiving quality informationbetween the respective pilot channels is smaller than the lower limitthreshold value, determines to decrease the pilot channels in thedirection of the frequency axis. Note that the common pilot channel maynot be deleted. Further, the upper limit threshold value described aboveand the lower limit threshold value explained above may be set into onethreshold value.

The frame requesting unit 111 next determines the allocation of thepilot signals according to the Pattern 2. The frame requesting unit 111acquires each difference in the receiving quality information betweenthe neighboring pilot channels in the direction of the time axis. Theexample in FIG. 2 is that only the common pilots exist in the frame, andtherefore the difference between the pilot channel in the frame atTTI(n) and the pilot channel in the frame at TTI(n+1) is obtained inevery subcarrier. Specifically, the differences in the receiving qualityinformation between the respective pilot channels in the direction ofthe time axis are acquired such as obtaining the difference between thereceiving quality information of the pilot channel P1 and the receivingquality information of the pilot channel P11 and further obtaining thedifference between the receiving quality information of the pilotchannel P2 and the receiving quality information of the pilot channelP12.

The frame requesting unit 111, when obtaining each difference in thereceiving quality information between the respective pilot channels,further acquires an average value of these differences in the receivingquality information therebetween, and compares this average value withthe previously retained upper limit threshold value. The upper limitthreshold value may involve using the same value as in the Pattern 1 andmay also involve taking another value. The frame requesting unit 111, ifthe average value exceeds the upper limit threshold value, determines toincrease the pilot channels in the direction of the time axis. As aresult of the determination thus made, the radio frame to be transmittedfrom the transmitting device becomes as illustrated in FIG. 4. FIG. 4 isa diagram showing an example of the pilot channel allocation to bechanged as the result of the determination of the frame requesting unit111. The example in FIG. 4 shows an addition of the pilot channels(P1-01, P2-01, P3-01, P4-01, P5-01) in the direction of the time axis ofthe radio frame.

Thus, when the process in the Pattern 1 and the process in the Pattern 2are executed each once, the pilot channel allocation becomes as shown inFIG. 5. FIG. 5 is a diagram showing the pilot channel allocation to bechanged as a result of combining the process in the Pattern 1 with theprocess in the Pattern 2. The frame requesting unit 111, in the case ofincreasing the pilot channels in the direction of the time axisaccording to the Pattern 2, increases the pilot channels in a sequenceshown in FIG. 6. FIG. 6 is a chart showing the sequence of increasingand decreasing the pilot channels in the direction of the time axis. Thesequence is indicated by numeral values bracketed in FIG. 6. Asdescribed above, in the examples of the pilot channels allocations inFIGS. 4 and 5, the pilot signal is allocated to the channel indicated bya sequential number (1). Accordingly, in FIGS. 4 and 5, when furtherincreasing the pilot channel in the direction of the time axis, itfollows that the channel indicated by a sequential number (2) isdetermined to be the pilot channel.

Conversely when decreasing the number of the pilot channels, the pilotchannels are decreased in a descending sequence organized by thesequential numbers shown in FIG. 6. The lower limit threshold value isutilized for the determination of decreasing the pilot channels in thedirection of the time axis in the same way as in the Pattern 1 describedabove.

The frame requesting unit 111 previously retains a second upper limitthreshold value (corresponding to a predetermined upper limit thresholdvalue according to the present invention) in addition to the upper limitthreshold value and the lower limit threshold value described above. Theframe requesting unit 111, when judging that each of the differences inthe receiving quality information between the respective pilot channels,which are obtained by the processes in the Patterns 1 and 2 describedabove, exceeds the upper limit threshold value, determines to requirethe all-pilot frame (Pattern 3). FIG. 7 is a diagram showing an exampleof a structure of the all-pilot frame. Note that FIG. 7 illustrates onlyone frame as the all-pilot frame, however, a plurality of all-pilotframes may also be continuously or discontinuously transmitted. Theframe requesting unit 111 transfers the information of the pilot channelallocations determined according to the Patterns 1, 2 and 3 describedabove to the transmitting unit 112 and the channel estimation unit 105.

It is to be noted that the frame requesting unit 111, when receiving theall-pilot frame, executes the process in the Pattern 1 explained aboveand the process in the Pattern 2 described above with respect to thereceiving quality information on all the pilot channels. Through thisprocessing, the all-pilot frame comes to have a proper pilot channelallocation in a way that gradually decreases the pilot channelscorresponding to a propagation environment.

The transmitting unit 112 generates the radio frame in which the pilotchannel allocation information transferred from the frame requestingunit 111 is allocated to a control channel. The generated radio frame istransmitted from the transmitting antenna 120. The pilot channelallocation information generated by the transmitting unit 112 isallocated, in the form of bit data as shown in FIG. 8, to the controlchannel. FIG. 8 is a table showing an example of notification of thepilot channel allocation information. In the example in FIG. 8, a bitrepresenting a process in the direction of the frequency axis, a bitrepresenting a process in the direction of the time axis, a bitrepresenting an addition/reduction of the pilot symbols, a bitrepresenting a status and a bit representing an all-pilot request arearranged in a direction from a least significant bit (which willhereinafter be abbreviated to LSB) to a most significant bit (which willhereinafter be abbreviated to MSB).

The transmitting unit 112, when receiving an increase request in thedirection of the frequency axis from the frame requesting unit 111,generates the pilot channel allocation information, wherein “1” is setin the bit representing the process in the direction of the frequencyaxis, “0” is set in the bit representing the process in the direction ofthe time axis, “0” is set in the bit representing the addition/reductionof the pilot symbols, “1” is set in the bit representing the status, and“0” is set in the bit representing the all-pilot request. Thetransmitting unit 112, conversely when receiving a decrease request inthe direction of the frequency axis from the frame requesting unit 111,generates the pilot channel allocation information, wherein “1” is setin the bit representing the process in the direction of the frequencyaxis, “0” is set in the bit representing the process in the direction ofthe time axis, “1” is set in the bit representing the addition/reductionof the pilot symbols, “1” is set in the bit representing the status, and“0” is set in the bit representing the all-pilot request. Further, whenreceiving an all-pilot request, the transmitting unit 112 generates thepilot channel allocation information, wherein “1” is set in the bitrepresenting the all-pilot request. Note that the transmitting unit 112,when receiving a request for retaining a status of the last time fromthe frame requesting unit 111, generates the pilot channel allocationinformation, wherein “0” is set in the bit representing the process inthe direction of the frequency axis, “0” is set in the bit representingthe process in the direction of the time axis, “0” is set in the bitrepresenting the status, and “0” is set in the bit representing theall-pilot request.

[Transmitting Device]

The transmitting device in the embodiment of the present invention willhereinafter be explained with reference to FIG. 9. FIG. 9 is a diagramillustrating a functional configuration of the transmitting device inthe present embodiment.

The transmitting device in the present embodiment includes atransmitting antenna 200, a transmitting unit 201 (corresponding totransmitting unit according to the present invention), a parallel/serial(which will hereinafter be abbreviated to P/S) converting unit 202, aninverse discrete Fourier transform (which will hereinafter beabbreviated to IDFT) unit 203, a serial/parallel (which will hereinafterbe abbreviated to S/P) converting unit 204, a multiplexing unit(corresponding to allocation unit according to the present invention)205, a user data generating unit 206, a pilot generating unit 207, acontrol channel demodulating/decoding unit 208, a receiving unit 209, areceiving antenna 210, and so on.

The signals containing the pilot channel allocation informationtransmitted from the receiving device described above are received bythe receiving antenna 210 and are transmitted to the receiving unit 209.The receiving unit 209 executes predetermined signal processing (such asbaseband signal conversion, analog/digital conversion and thesynchronous detection demodulation) with respect to the received radiofrequency signals, and transfers a control channel signal in theoutputted signals to the control channel demodulating/decoding unit 208.

The control channel demodulating/decoding unit 208 demodulates anddecodes the control channel signal received from the receiving unit 209,and acquires the pilot channel allocation information (FIG. 8) containedin the control channel signal. The thus-acquired pilot channelallocation information is transmitted to the multiplexing unit 205 andto the pilot generating unit 207.

The user data generating unit 206 generates a user data signal to begiven to the receiving device serving as a transmitting destination. Thegenerated user data signal is transferred to the multiplexing unit 205.The pilot generating unit 207 generates the pilot signal on the basis ofthe pilot channel allocation information transferred from the controlchannel demodulating/decoding unit 208. The generated pilot signal istransferred to the multiplexing unit 205.

The multiplexing unit 205 determines the allocation of the pilotchannels of the transmitting radio frame on the basis of the pilotchannel allocation information transferred from the control channeldemodulating/decoding unit 208, i.e., the pilot channel allocationinformation shown in FIG. 8, which has been transmitted from thereceiving device described above, and multiplexes the pilot signaltransmitted from the pilot generating unit 207 with the user data signaltransmitted from the user data generating unit 206. Specifically, themultiplexing unit 205 retains the pilot channel allocation informationabout the present transmitting radio frame and reflects, in this pilotchannel allocation information, pieces of information described in thepilot channel allocation information shown in FIG. 8. The radio framemultiplexed with the pilot symbols by the multiplexing unit 205 isformed in the way exemplified in FIGS. 2 through 5.

The multiplexing unit 205, when “1” is set in the bit representing theall-pilot request in the pilot channel allocation information, generatesthe all-pilot frame illustrated in FIG. 7. The multiplexing unit 205, itfollows, does not multiplex the user data signal in the all-pilot frame.The signals multiplexed by the multiplexing unit 205 are transferred tothe S/P converting unit 204.

The S/P converting unit 204 converts serial signals generated by themultiplexing unit 205 into parallel signals arranged in parallelcorresponding to the number of the subcarriers. The IDFT unit 203executes an IDFT process with respect to the parallel signals outputtedfrom the S/P converting unit 204 on the unit of every OFDM symbol. Theon-the-time-axis signals carried on the respective subcarriers, whichare outputted from the IDFT unit 203, are synthetically multiplexed bythe P/S converting unit 202 and then transmitted to the transmittingunit 201. The transmitting unit 201 converts the serial signalstransmitted from the P/S converting unit 202 into the analog signals,then converts a central frequency of the signals into a radiotransmission frequency, and transmits the signals from the transmittingantenna 200.

It should be noted that the receiving device and the transmitting devicein the present embodiment discussed above use the IDFT for thefrequency-time transform process and the DFT for the time-frequencytransform process, however, the present invention does not limit thesemethods, wherein the frequency-time transform process may involve usinginverse fast Fourier transform (IFFT), and the time-frequency transformprocess may involve using fast Fourier transform (FFT).

Operational Example

Next, an operational example of the receiving device in the presentembodiment will be explained with reference to FIGS. 10 and 11. FIGS. 10and 11 are flowcharts showing the operational example of how the pilotchannel allocation is determined in the receiving device.

The receiving device in the present embodiment executes thepredetermined signal processing with respect to the radio transmissionfrequency signals received by the receiving antenna 100 (the receivingunit 101), and converts the digital signals obtained by this signalprocessing into the parallel signals (the S/P converting unit 101). Theparallel signals are Fourier-transformed by the DFT unit 102, and thesignals corresponding to the respective subcarrier components areoutputted (the DFT unit 102). The channel estimation unit 105 compareseach of the pilot symbols allocated to the pilot channels in the signalscorresponding to the respective subcarrier components with the knownpilot signal, thereby performing the channel estimation about the pilotchannel (S1001).

Next, the receiving quality information generating unit 110 generatesthe receiving quality information about the pilot channel on the basisof the channel estimation value given from the channel estimation unit105 or the CRC bit given from the decoding unit 106 (S1002). Thereceiving quality information is exemplified such as the SINR, the SNRand the bit error rate.

The frame requesting unit 111, upon receiving the receiving qualityinformation, executes at first the process according to the Pattern 1described above, i.e., the process of changing the pilot channels in thedirection of the frequency axis. The frame requesting unit 111 obtainseach difference in the receiving quality information between therespective neighboring pilot channels in the direction of the frequencyaxis (S1003). Then, the frame requesting unit 111 acquires the averagevalue of the thus-obtained differences in the receiving qualityinformation therebetween (S1004). Subsequently, the frame requestingunit 111 compares the average value of the thus-obtained differences inthe receiving quality information in the direction of the frequency axiswith the previously retained upper limit threshold value (S1005). Theframe requesting unit 111, when judging from this comparison that theaverage value exceeds the upper limit threshold value (S1005; YES),further judges whether or not the average value exceeds the second upperlimit threshold value (S1006). The frame requesting unit 111, whenjudging from this comparison that the average value exceeds the secondupper limit threshold value (S1006; YES), determines the request for theall-pilot frame (S1007). While on the other hand, the frame requestingunit 111, when judging from this comparison that the average value doesnot exceed the second upper limit threshold value (S1006; NO),determines to increase the pilot channels in the direction of thefrequency axis (S1008).

The frame requesting unit 111, when judging that the average value doesnot exceed the upper limit threshold value (S1005; NO), further judgeswhether or not the average value is smaller than the lower limitthreshold value (S1009). The frame requesting unit 111, when judgingfrom this comparison that the average value is smaller than the lowerlimit threshold value (S1009; YES), determines to decrease the pilotchannels in the direction of the frequency axis (S1011). While on theother hand, the frame requesting unit 111, when judging that the averagevalue is not smaller than the lower limit threshold value (S1009; NO),determines to maintain the present state, i.e., the present pilotchannel allocation in the direction of the frequency axis (S1010).

The frame requesting unit 111, upon completing the process of changingthe pilot channels in the direction of the frequency axis (“A” depictedin FIGS. 10 and 11), executes next the process according to the Pattern2 described above, i.e., the process of changing the pilot channels inthe direction of the time axis. Note that if the request for theall-pilot frame is determined from the previous judgment, none of theprocess related to the Pattern 2 is executed (“B” depicted in FIGS. 10and 11).

The frame requesting unit 111 obtains each difference in the receivingquality information between the respective neighboring pilot channels inthe direction of the time axis (S1020). Then, the frame requesting unit111 acquires the average value of the thus-obtained differences in thereceiving quality information therebetween (S1021). Subsequently, theframe requesting unit 111 compares the average value of thethus-obtained differences in the receiving quality information in thedirection of the time axis with the previously retained upper limitthreshold value (S1022). The frame requesting unit 111, when judgingfrom this comparison that the average value exceeds the upper limitthreshold value (S1022; YES), further judges whether or not the averagevalue exceeds the second upper limit threshold value (S1023). The framerequesting unit 111, when judging from this comparison that the averagevalue exceeds the second upper limit threshold value (S1023; YES),determines the request for the all-pilot frame (S1024). While on theother hand, the frame requesting unit 111, when judging from thiscomparison that the average value does not exceed the second upper limitthreshold value (S1023; NO), determines to increase the pilot channelsin the direction of the time axis (S1025).

The frame requesting unit 111, when judging that the average value doesnot exceed the upper limit threshold value (S1022; NO), further judgeswhether or not the average value is smaller than the lower limitthreshold value (S1026). The frame requesting unit 111, when judgingfrom this comparison that the average value is smaller than the lowerlimit threshold value (S1026; YES), determines to decrease the pilotchannels in the direction of the time axis (S1027). While on the otherhand, the frame requesting unit 111, when judging that the average valueis not smaller than the lower limit threshold value (S1026; NO),determines to maintain the present state, i.e., the present pilotchannel allocation in the direction of the time axis (S1028).

The frame requesting unit 111 generates the pilot channel allocationinformation on the basis of the thus-determined content (S1029), andtransmits this pilot channel allocation information to the channelestimation unit 105 and to the transmitting unit 112. The channelestimation unit 105 detects, based on this pilot channel allocationinformation, the allocation of the pilot channels in regard to therespective signals transmitted from the DFT unit 102. The transmittingunit 112 generates the radio frame in which the pilot channel allocationinformation transferred from the frame requesting unit 111 is allocatedto the control channel, and transmits this radio frame. The transmittingunit 112, on the occasion of generating the radio frame, sets the pilotchannel allocation information as the bit data shown in FIG. 8.

The transmitting device receiving the radio frame containing this pilotchannel allocation information comes to transmit, hereafter, the radioframe having the pilot channel allocation based thereon. Namely, themultiplexing unit 205 of the transmitting device multiplexes, based onthis pilot channel allocation information, the pilot signal generated bythe pilot generating unit 207 with the user data signal generated by theuser data generating unit 206. The multiplexing unit 205, if the pilotchannel allocation information is data that prompts the transmittingdevice to change the pilot channels in the direction of the time axis,determines the pilot channel allocation in the sequence shown in, e.g.,FIG. 6. Further, the multiplexing unit 205, if the pilot channelallocation information is the data representing the request for theall-pilot frame, outputs the all-pilot frame that does not involvemultiplexing the user data signal.

Note that the receiving device receiving the all-pilot frame, thereceiving quality information on all the pilot channels being generated,executes the process in the Pattern 1 and the process in the Pattern 2with respect to this generated receiving quality information on all thepilot channels. Through this processing, the all-pilot frame comes tohave the proper pilot channel allocation in a way that graduallydecreases the pilot channels corresponding to the propagationenvironment.

Operation/Effect in First Embodiment

In the receiving device in the present embodiment, when receiving theOFDM signals transmitted from the transmitting device, the predeterminedsignal processing is executed with respect to these receiving signals,whereby the signals corresponding to the respective subcarriercomponents are outputted. In the receiving signals, the plural pilotsignals are allocated at the predetermined intervals respectively in thedirection of the time axis and in the direction of the frequency axis,and the channel estimation unit 105 performs the channel estimation withrespect to each pilot channel by use of the pilot symbol allocated tothe pilot channel in the signals corresponding to the individualsubcarrier components. Subsequently, the receiving quality informationgenerating unit 110 generates the receiving quality information (forexample, the SINR, the SNR and the BER) related to each pilot channel byusing the channel estimation value or the CRC bit given from thedecoding unit 106.

The frame requesting unit 111 executes at first, based on the receivingquality information on each pilot channel, the process (the Pattern 1)of changing the number of the pilot channels in the direction of thefrequency axis. The process according to this Pattern 1 involvesobtaining each difference in the receiving quality information betweenthe respective neighboring pilot channels in the direction of thefrequency axis and acquiring the average value of the thus-obtaineddifferences in the receiving quality information therebetween. Thethus-acquired average value of the differences in the receiving qualityinformation in the direction of the frequency axis is compared with thepre-retained upper limit threshold value, the pre-retained second upperlimit threshold value and the pre-retained lower limit threshold value,thereby determining the contents of how the number of the pilot channelsin the direction of the frequency axis is changed. Namely, the requestfor the all-pilot frame is determined in the case of AverageValue>Second Upper Limit Threshold Value>Upper Limit Threshold Value,the increase in the pilot channels in the direction of the frequencyaxis is determined in the case of Second Upper Limit ThresholdValue≧Average Value>Upper Limit Threshold Value, the decrease in thepilot channels in the direction of the frequency axis is determined inthe case of Lower Limit Threshold Value>Average Value, and none of thechange (present state) in the pilot channels in the direction of thefrequency axis is determined in other cases.

Next, the frame requesting unit 111 executes, based on the receivingquality information on each pilot channel, the process (the Pattern 2)of changing the number of the pilot channels in the direction of thetime axis. The process according to this Pattern 2 involves obtainingeach difference in the receiving quality information between therespective neighboring pilot channels in the direction of the time axisand acquiring the average value of the thus-obtained differences in thereceiving quality information therebetween. The thus-acquired averagevalue of the differences in the receiving quality information in thedirection of the time axis is compared with the pre-retained upper limitthreshold value, the pre-retained second upper limit threshold value andthe pre-retained lower limit threshold value, thereby determining thecontents of how the number of the pilot channels in the direction of thetime axis is changed. The detailed determination method is the same asby the Pattern 1.

The pilot channel allocation information is generated based on thethus-determined contents of how the pilot channels are changed, andthere is transmitted the radio frame in which this pilot channelallocation information is allocated to the control channel. Further, thechannel estimation unit 105 utilizes this pilot channel allocationinformation in order to know the allocation of the pilot channels in thereceived signals.

The transmitting device in the present embodiment, when receiving theradio frame containing the pilot channel allocation information,transmits hereafter the radio frame in which this pilot channelallocation information is reflected. Note that, in this case, if thepilot channel allocation information is the data representing therequest for the all-pilot frame, there is outputted the all-pilot framethat does not involve multiplexing the user data signal.

Thus, in the present embodiment, the receiving device determines, basedon the receiving quality information on the respective pilot channels,the pilot channel allocation information containing the necessary numberof the pilot channels etc, and notifies the transmitting device of thepilot channel allocation information, while the transmitting devicetransmits the radio frame in which the notified pilot channel allocationinformation is reflected.

Therefore, it is possible to take the pilot channel allocatingconfiguration corresponding to the channel propagation environment, toimprove the communication performance such as the receiving error rateand to prevent a decrease in the transmission rate that is caused by afutile allocation of the pilot channels. Moreover, the control isexecuted so as to take the proper pilot channel allocating configurationcorresponding to the now-and-then propagation environment, whereby thedevice can be made less likely to be affected by fading that depends onthe propagation environment etc.

Especially when the difference in the receiving quality informationbetween the respective pilot channels rises, i.e., even in such a casethat the fading exerts large influence, it follows that the control isperformed so as to promptly take the proper pilot channel allocation dueto the all-pilot frame request determined based on the second upperlimit threshold value larger than the upper limit threshold value.

Others

The disclosures of Japanese patent application No. JP2006-074359, filedon Mar. 17, 2006 including the specification, drawings and abstract areincorporated herein by reference.

1. A communication system, comprising: a receiving device including: atransmitting unit which transmits configuration information indicativeof allocations, in a direction of a frequency axis, of pilot signals ina signal to be transmitted from a transmitting device; and a receivingunit which receives a signal transmitted from the transmitting device inwhich the pilot signals are allocated based on the configurationinformation transmitted by the receiving device; and the transmittingdevice including: a receiving unit which receives the configurationinformation from the receiving device; and a transmitting unit whichtransmits the signal to the receiving device in which the pilot signalsare allocated based on the configuration information received from thereceiving device.
 2. A communication system, comprising: a receivingdevice including: a notifying unit which transmits a requesting signalindicative of a number of pilot signals, used for generating receivingquality information, in a direction of a frequency axis in a signal tobe transmitted from a transmitting device; and a receiving unit whichreceives a signal from the transmitting device in which the pilotsignals are allocated based on the requesting signal transmitted by thereceiving device; and the transmitting device including: an allocationunit which determines allocations, in the direction of the frequencyaxis, of the pilot signals based on the requesting signal; and atransmitting unit which transmits the signal having the determinedallocations of the pilot signals.